#### Means

d
```package com.thealgorithms.maths;

import java.util.stream.StreamSupport;
import org.apache.commons.collections4.IterableUtils;

/**
* https://en.wikipedia.org/wiki/Mean
* <p>
* by: Punit Patel
*/
public final class Means {

private Means() {
}

/**
* @brief computes the [Arithmetic Mean](https://en.wikipedia.org/wiki/Arithmetic_mean) of the input
* @param numbers the input numbers
* @throws IllegalArgumentException empty input
* @return the arithmetic mean of the input numbers
*/
public static Double arithmetic(final Iterable<Double> numbers) {
checkIfNotEmpty(numbers);
return StreamSupport.stream(numbers.spliterator(), false).reduce((x, y) -> x + y).get() / IterableUtils.size(numbers);
}

/**
* @brief computes the [Geometric Mean](https://en.wikipedia.org/wiki/Geometric_mean) of the input
* @param numbers the input numbers
* @throws IllegalArgumentException empty input
* @return the geometric mean of the input numbers
*/
public static Double geometric(final Iterable<Double> numbers) {
checkIfNotEmpty(numbers);
return Math.pow(StreamSupport.stream(numbers.spliterator(), false).reduce((x, y) -> x * y).get(), 1d / IterableUtils.size(numbers));
}

/**
* @brief computes the [Harmonic Mean](https://en.wikipedia.org/wiki/Harmonic_mean) of the input
* @param numbers the input numbers
* @throws IllegalArgumentException empty input
* @return the harmonic mean of the input numbers
*/
public static Double harmonic(final Iterable<Double> numbers) {
checkIfNotEmpty(numbers);
return IterableUtils.size(numbers) / StreamSupport.stream(numbers.spliterator(), false).reduce(0d, (x, y) -> x + 1d / y);
}

private static void checkIfNotEmpty(final Iterable<Double> numbers) {
if (!numbers.iterator().hasNext()) {
throw new IllegalArgumentException("Emtpy list given for Mean computation.");
}
}
}
```